Leaded silicon manganese bearing brass



Aug. 22, 1967 T. E. FEARNSIDE 3,337,335

I LEADED SILICON MANGANESE BEARING BRASS Filed June 8, 1964 2 Sheets-Sheet 1 ,8 PB SILICIDE a QC 5 PB Sgucgo INVENTOR THOMAS E. FEARNSIDE ATTORNEYS T. E. FEARNSEDE LEADED SILICON MANGANESE BEARING BRASS Aug. 22, 1967 2 Sheets-Sheet 2 Filed June 8, 1964 FIG u W F INVENTOR THOMAS E FEARNSIDE ATTORNEYS United States Patent 3,337,335 LEADED SILICON MANGANESE BEARING BRASS Thomas E. Fearnside, Port Huron, Mich., assignor to Mueller Brass Company, Port Huron, Mich., a corporation of Michigan Filed June 8, 1964, Ser. No. 373,438 8 Claims. (Cl. 75--157.5)

This invention relates to a bearing alloy, and more particularly to a leaded silicon manganese bearing brass containing nickel.

For many years bearing brasses of the 60 copper-40 zinc type containing manganese and silicon have been in widespread use. One such alloy is disclosed in Vaders Patent No. 2,145,065. These bearing brasses containing silicon and manganese are characterized in their microstructure by the presence of hard particles of manganese silicide in the alpha plus beta duplex matrix. These hard particles have been identified as Mn Si and they they appear as a long, needle-like structure randomly distributed and oriented. Such prior art alloys are capable of being hot extruded, hot forged and cold drawn, as well as being capable of heat treatment to increase their mechanical properties. Experience has shown, however, that working and heat treatment of these alloys does not substantially aflYect the needle-like structure of the manganese silicide particles. Furthermore, the increase of mechanical properties of these alloys by heat treatment is subject to serious limitations, because of the uncontrolled grain growth that occurs upon heating the alloys to a quenching temperature sufiiciently high to obtain the mechanical properties desired. Normally heat treating of such alloys is accomplished by heating to 1300 F., holding at that temperature for several minutes and then cooling rapidly by quenching in water or oil. Heating such alloys to 1300 F. causes the alpha plus beta phase to transform to the beta phase, or at least to a predominantly beta phase. Quenching retains the beta structure in a metastable condition to a large degree, thus producing a hardening eliect. Tempering this structure at 600 F. to 800 F. increases the mechanical properties of the alloy through a mechanism of retransforming the metastable beta to fine alpha particles in a beta matrix. However, in View of the uncontrolled grain growth which occurs upon heating such alloys to effect hardening upon quenching, it has always been necessary to closely control the chemical composition, forging temperature, degree of mechanical working and the heat treating conditions to which the alloys are subjected.

In addition to the problem resulting from uncontrolled grain growth upon heating of such alloys, experience has shown that while the hard manganese silicide particles in a softer matrix are desirable from the standpoint of the bearing qualities of the alloy, nevertheless fatigue failures, presumably due to the needle-like structure and the brittleness of the manganese silicide particles are not uncommon in parts formed from such alloys.

It is an object of the present invention to improve the bearing, mechanical and fabricating properties of such alloys. More specifically, the invention contemplates the addition to such alloys of nickel within a relatively narrow range of composition, a range much narrower than the .05 to 3% suggested in the above-referred-to Vaders patent. The compositional limits of the other elements in the improved alloy are also much narrower than disclosed in the Vaders patent, in order to obtain the improved mechanical properties of the alloy.

In the drawings:

FIGS. 1, 3 and 5 show microstructures of a typical prior art alloy in the as cast, hot forged and heat treated conditions, respectively.

FIGS. 2, 4 and 6 show the microstructures of the improved alloy in the as cast, hot forged and heat treated conditions, respectively.

FIG. 7 shows a series of macrostructures illustrating the grain growth which occurs in the prior art alloy upon heat treating samples which have been worked in progressively increasing amounts.

FIG. 8 shows a series of macrostructures illustrating the effect on grain growth in the improved alloy of heat treating of a series of samples which have been worked in progressively increasing amounts.

The conventional alloy illustrated in FIGS. 1, 3, 5 and 7 falls into the group of alloys having the following composition:

TABLE I Percent Copper 58.5-61 Silicon .7-1.3 Manganese 2.0-3.0 Lead .5-1.5 Zinc Balance The composition of the alloy illustrated in FIGS. 1, 3, 5 and 7 is approximately as follows:

TABLE II Percent Copper 59.30 Lead 1.13 Silicon .93 Manganese 2.45 Nickel .05 Iron .16 Zinc Balance The improved alloy of the present invention has the following nominal composition:

TABLE III Percent Copper 55.70-57.70 Silicon .701.3 Manganese 2.03.0 Nickel 1.6-2.4 Lead .50-1.0 Zinc Balance The composition of the alloy shown in FIGS. 2, 4, 6 and 8 is approximately as follows:

TABLE IV Percent Copper 57.42 Silicon .94 Manganese 2.14 Nickel -Q 2.32 Lead .74 Iron .17 Zinc Balance In these alloys iron is considered an impurity, since in substantial amounts it adversely aifects the forging properties. Iron is therefore maintained at less than .25 percent. While the presence of small amounts of tin is more beneficial than harmful to the alloy, nevertheless the cost of tin does not warrant its inclusion in the alloy as an addition, in view of its negligible improvement in mechanical properties relative to the cost of the tin addition.

In comparing the nominal composition of the improved alloy as set forth in Table III with the nominal composition of the prior art alloy, as set forth in Table I, the primary difi'erences are quite evident. The improved alloy contains nickel in the amount of 1.6 to 2.4%, whereas in the conventional alloy nickel is present only in a very negligible amount, if any. Likewise, in the improved alloy, the highest permissible percentage of copper is below the lowest percentage of copper in the prior art alloy.

In comparing the microstructures of the conventional alloy, as shown in FIGS. 1, 3 and 5, with that of the improved alloy, as shown in FIGS. 2, 4 and 6, the differences are readily apparent. For example, in comparing the as cast structure in FIG. 1 with the as cast structure in FIG. 2, the manganese silicide of the conventional alloy appears as a long, needle-like structure with sharp pointed ends. In the improved alloy, as shown in FIG. 2, it is apparent that the addition of nickel has broken up the manganese silicide particles, so that they are no longer in the form of the long, needle-like structure which characterizes the conventional alloy. In the improved alloy the silicide particles tend to be located in a grain boundary type of pattern, as probably influenced by the original dendritic structure of the casting. As is evident from FIG. 2, the manganese silicide particles appear to have a more amorphous form than the definite needle-like structure of the conventional alloy, and the ends of the silicide particles are rounded rather than sharp pointed, as is the case with the conventional alloy. Hot working of the alloy by extrusion or forging, as shown in FIG. 4, results in the breakup of the silicide particles to a more spheroidal form than in the as cast condition, and a more random distribution than in the as cast condition. This configuration and distribution of the silicide particles in the improved alloy is more desirable, in that it eliminates the potential notch effect of the elongated needle-like particles in the conventional alloy. Furthermore, since the silicides in the improved alloy are not decidedly elongated, more uniform properties between longitudinal and transverse directions are obtainable. In the heat treated condition of the improved alloy (FIG. 6), the matrix is similar to that of the conventional alloy (FIG. but in all cases it should be noted that the silicide particles in the improved alloy do not take the form of the needlelike structure, as is the case in the conventional alloy, but rather assume a spheroidal type structure. Although some of the silicide particles may be slightly elongated, nevertheless they still have a spheroidal type shape on their ends, and this will tend to alleviate the tendency toward notch effects caused by sharp angles.

A very important feature of the improved alloy resides in a very substantial retardation of grain growth upon hot working followed by heat treatment, as compared with the conventional alloy. This difference between the improved alloy and the conventional alloy is clearly apparent from a comparison of FIGS. 7 and 8. In both of these figures the sample at the left of the top row represents the extruded condition, while the sample second from the left of the top row represents the extruded and heat treated condition. The remaining samples illustrate the effect on grain growth of progressively increasing hot working followed by heat treatment. Although the grain growth is not entirely eliminated with the improved alloy, nevertheless the very substantial improvement on the all-over grain size and the small degree of grain growth is clearly evident. Experience in production of this alloy has shown that grain growth problems on heat treating have been substantially entirely eliminated. The retardation in grain growth in the improved alloy can be attributed to the fact that the nickel addition displaces the composition in the copper-zinc constitution diagram toward the copper end of the diagram. This allows higher heat treating temperatures in a more rich alpha and less rich beta portion of the alpha plus beta phase field. Grain growth problems increase as a copperzinc alloy approaches the all-beta condition.

Nickel is mutually soluble in cop-per at all compositions in the liquid and solid states. Thus the nickel addition to the copper-zinc alloy improves its mechanical properties to some extent through solid solution. Tests have shown a very slight increase in the matrix hardness by the addition of nickel in the range referred to in the improved alloy. It appears that the beta phase is the one most affected by the nickel addition, resulting in a 20% increase in the measured Knoop hardness in the as cast condition. For example, a hardness of 142 Knoop was obtained with the conventional alloy under a 2 gram load, Whereas a hardness of 171 Knoop was obtained with an alloy containing approximately 2% nickel. Similar increases in hardness are experienced in the other processed conditions of the improved alloy, as compared with the conventional alloy. However, the increase in hardness of the matrix because of the nickel addition is not of primary importance.

With respect to the mechanical properties of the alloy,

nickel exhibits its most pronounced effect on the hardness of the silicide particles. For example, with the conventional alloy shown in FIGS. 1, 3 and 5, a Knoop hardness of 1138 of silicide particles was obtained under a 2 gram load. With the improved alloy shown in FIGS. 2, 4 and 6, a Knoop hardness of 802 of the silicide particles was obtained. Lowering of the hardness of the silicide particles increases their ductility, and this accounts for the fact that the improved alloy has better wear-in properties against a steel mating surface, a very important factor in bearing parts. This allows the use of a somewhat softer steel mating surface than would otherwise be possible,

which in turn increases the latitude of control allowable in the designing of bearing applications. Experience has shown that with the improved alloy, by reason of the reduced brittleness of the silieides, there is less tendency toward silicide breakup and breakaway of the silicide particles from the matrix. The alloy thus exhibits substantially improved properties in bearing applications, particularly with respect to its sliding friction properties in high-pressure, high-speed applications. The alloy also exhibits better resistance to cavitation erosion in the case of high-pressure fluid pumps.

The effect of nickel on lowering the hardness of the manganese silicide particles indicates the probability that the nickel not only enters into solution with the copper in the alloy but also forms an intermetallic compound with the silicon and manganese. The intermetallic compound is not only softer than Mn Si but also has a different crystal structure, a more amorphous form, than Mn Si as is indicated by a comparison of FIGS. 1 and 2.

The most outstanding improvement in mechanical properties of the improved alloy of this invention lies in its fatigue characteristics. Tests have shown that the improved alloy will withstand a 15% higher stress at a total of 100,000,000 cycles of reversed loading, as determined on the R. R. Moore type rotating beam fatigue machines. For example, the conventional alloy will withstand 35,000 p.s.i. while the improved alloy will withstand 40,000 p.s.i. at 100,000,000 cycles. This improvement in the fatigue stress of the improved alloy can be attributed to the effect of nickel on the solid solution hardening, the increase in the allowable heat treating temperature and the decrease in the silicide hardness and improvement in configuration. The increase in hardness of the matrix by reason of the nickel addition has been referred to. As explained previously, although the nickel obviously affects the formation of the silicide particles, undoubtedly some nickel is available for increasing the matrix hardness slightly. Tests have shown that increasing nickel additions to the alloy produce progressively slightly higher hardnesses of the matrix. The increase in the allowable heat treating temperature is attributed to the fact that the composition in the copper-zinc constitution diagram is displaced toward the copper end. A higher temperature allows more alpha to transform to beta upon heating with the subsequent potential of more alpha transforming from the metastable beta on quenching. Naturally, the larger the amount of alpha available for transformation, the higher are the potential strength and hardness properties available.

The desirable properties of this alloy are obtainable only if the nickel content of the alloy is maintained within the close limits specified above in Table III. If the nickel content of the alloy falls below 1.6%, the amount of breakup of the needle-like structure of the silicide particles of the conventional alloy will not be suflicient to elfect a substantial improvement in the microstructure of the alloy. On the other hand, if the nickel content of the alloy exceeds 2.4%, the hardness of the silicide particles will be too low to achieve the desired bearing properties. For example, as pointed out above, with the conventional alloy containing substantially .05% nickel, a Knoop hardness of 1138 of the silicide particles under a 2 gram load is obtained. With the improved alloy, containing about 2.3% nickel, the Knoop hardness dropped to 802, and when the nickel was increased to about 3%, the Knoop hardness dropped to about 703.

To obtain the desired microstructures in the alloy and to develop the desirable mechanical properties, it is necessary not only to produce an alloy having a composition lying within the ranges set forth in Table III, but also to proceed through casting and hot working of the alloy either by extrusion or by hot pressing. The alloy is adapted for use in the form of rod, tubing or hot pressed parts. The improved alloy is capable of being drawn to as much as a 50% reduction in area without intermediate anneals. The drawn or extruded rod or the hot pressing are preferably heat treated to obtain the higher and more uniform properties. Hot extrusion and hot pressing of the alloys are best accomplished between 1200 F. and 1300 F., and the heat treating is best accomplished by quenching in water from 1350 F. to 1450 F., followed by a 500 F. to 800 F. temper and air cooling. This quenching temperature is 50 F. to 150 F. higher than employed with the conventional alloy and does not present any serious problem of grain growth. The samples shown in FIGS. 7 and 8 were quenched from 1350 F.

The melting practice employed in the production of this alloy follows conventional practice. First a copper-zinc alloy melt is developed and then silicon and manganese are added to the melt as copper-silicon and copper-manganese alloy additions to obtain the desired silicon and manganese additions. Nickel is added directly to the copper-Zinc-silicon-manganese alloy, and lead may be added at any time during melting. Casting is best followed by hot extrusion with subsequent drawing or hot pressing operations and a final heat treatment.

The composition set forth in Table IV is one typical composition of the improved alloy, specifically the composition of the structures shown in FIGS. 2, 4 and '6. Other compositions lying within the range set forth in Table III have proved to possess the desirable properties discussed above. For example, one specific composition which has proved to be highly satisfactory is the following:

The above composition was hot extruded as a round rod, heat treated as above described and straightened. This material had a yield strength of 53,000 p.s.i. and an ultimate strength of 71,500 p.s.i., with an elongation of 18%. The core hardness was 81 Rockwell B and the surface hardness was 92 Rockwell B. This material proved to have excellent properties as bearing parts.

I claim:

1. A hearing alloy consisting essentially of 55.70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .50 to 1.0% lead, and the balance zinc.

2. A bearing alloy consisting essentially of 55.70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .50 to 1.0% lead, less than .25 iron and the balance zinc.

3. A hearing alloy consisting essentially of 57.42% copper, 94% silicon, 2.14% manganese, 2.32% nickel, .74% lead, .17% iron and the balance zinc.

4. An article of manufacture comprising a bearing part which has been subjected to hot working and comprising an alloy consisting essentially of 55.70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .50 to 1.0% lead and the balance zinc, the microstructure of said alloy being characterized by the presence of silicide particles randomly distributed throughout the matrix of the alloy and having a configuration varying between generally spheroidal and slightly elongated with rounded ends and edges, as distinguished from a highly elongated structure with sharp cornered angular ends.

5. An article of manufacture comprising a bearing part which has been subjected to hot working and comprising an alloy consisting essentially of 55.70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .50 to 1.0% lead and the balance zinc, the microstructure of said alloy being characterized by the presence of silicide particles randomly distributed throughout the matrix of the alloy, said silicide particles being generally rounded at their edges and being substantially more equiaxed than is representative of a needle-like structure.

6. An article of manufacture comprising a bearing part which has been subjected to hot working and comprising an alloy consisting essentially of 55 .70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .50 to 1.0% lead and the balance zinc, the microstructure of said alloy being characterized by the presence of silicide particles randomly distributed throughout the matrix of the alloy, said silicide particles being generally rounded at their edges and being substantially more equiaxed than is representative of a needl-like structure, said article having been heated to and quenched from a temperature of from 1350 F. to 1450" F. and tempered at from 500 F. to 800 F., the macrostructure being characterized by an overall relatively fine grain size.

7. An article of manufacture comprising a bearing part which has been subjected to hot working and comprising an alloy consisting essentially of 55.70 to 57.70% copper, .70 to 1.3% silicon, 2.0 to 3.0% manganese, 1.6 to 2.4% nickel, .5 0 to 1.0% lead and the balance zinc, the microstructure of said alloy being characterized by the presence of silicide particles randomly distributed throughout the matrix of the alloy, said silicide particles being generally rounded at their edges and being substantially more equiaxed than is representative of a needle-like structure, and the macrostructure being characterized by an overall relatively fine grain size.

'8. A hearing alloy consisting essentially of 56.51% copper, .9'1% silicon, 2.65% manganese, 2.1% nickel, .90% lead, .16% iron, 09% tin, .004% aluminum and the balance zinc.

DAVID L. RECK, Primary Examiner. R. O. DEAN, Assistant Examiner. 

1. A BEARING ALLOY CONSISTING ESSENTIALLY OF 55.70 TO 57.70% COPER, .70 TO 1.3% SILICON, 2.0 TO 3.0% MANGANESE, 1.6 TO 2.4% NICKEL, .50 TO 1.0% LEAD, AND THE BALANCE ZINC. 